Manufacture of rayon



Patented Aug. 31, 1943 UNITED STATES PATENT OFFICE 2,328,307 MANUFACTURE OF RAYON Asheville, and Edward tions rayon and more Gilbert I. Thurmond,

Brenner, Hendersonv American Enka Corpo poration of Delaware ille, N. C ration, Enka, N. 0., a corassignors to 7 Claims.

ention relates to the manufacparticularly to the prorayon thread of relatively high wet and dry state. Furtherviscose threads produced in accordance with the present invention, and other favorable have very low elongaproperties useful in the weaving and analogous arts.

Up to the spinning rayon th present time, the normal process for read has involved the use of a single acid coagulating bath. As distinguished from the said sin dustry is to utilize gle bath, the trend in the inthe so-called two-bath spinning system. Such a system includes a primary coagulating and partial regenerating bath, and a second bath in which further regeneration of the thread is effected taneously applied a relatively high found essential to while a high stretch is simulthereto. In order to carry out degree of stretch, it has been maintain the said second bath at a relatively high temperature, i. e., above 60 C. and preferably in the neighborhood 01' 80 C.

It is the general theory that this stretching, while passing the thread through a second bath dur-' ing regeneration, orients the micelles in the individual filaments and thereby increases the strength or tenacity of the finished thread.

In the two-bath system normally employed,

the coagulating bath contains an appreciable amount of sulphuric acid, as sulphuric acid efiects both generation of the it is well-known that coagulation and rethread. However, in order to impart a high degree of stretching in the second bath, the regeneration of the thread must be re tarded in the first bath, the form of its xanthate because the thread in has considerably higher elasticity and extensibility. In other words, the

extent to which I varies inversely with the In order to retard 780111 inthe flrstbath, it

to. metallic salts sulphate and ma the thread can be stretched degree of regeneration. the regenerative action of the is necessary-to add thereas sodium sulphate, zinc Obviously,

such gnesium sulphate.

the freshly extruded filaments constituting the thread must be s ufllciently coagulated in order to elongate the same in the form of line filaments and consequently,

a concentration or at tothe present invention, least 5% sulphuric acid prior has been used in the first bath.

Explanatory note.In patents and literature, and regenerating" ably and therefore,

the prior art including the terms coagulating" have been used interchangethe meaning has been contuned and misconstrued. The coagulation of viscoseisamoreorl ess physical change in the conversion of the viscose solutions into filaments wherein the thread is still in the form of cellulose xanthate which is chemically similar to viscose. The regeneration of the xanthate is the decomposition or conversion of cellulose xanthate into pure cellulose. I

Usually, 7% to 10% sulphuric acid is maintained in the first bath, and these amounts require a higher concentration of salts, zinc sulphate being the most efiective salt for retarding the regeneration of the xanthate. However, the use of zinc is objectionable for a number of reasons, one of which is that zinc can only retard the regeneration to a limited extent.

It is the object of the present invention to either eliminate the use of sulphuric acid in the primary coagulating bath, or to use sulphuric acid in concentrations suificiently low to prevent substantial regeneration of the cellulose xanthate even without employing metallic salts in conjunction therewith.

The invention further contemplates the utilization of a primary bath containing sumcient ammonium sulphate to coagulate viscose thread;

As a further object, the invention contemplates correlating the rate of regeneration of the cellulose xanthate with a high total stretch conducted in stages so as to provide a thread having a maximum degree of strength and a minimum elongation.

It has been determined in accordance with the present invention, that very low concentrations of sulphuric acid can be successfully used in the primary coagulating bath, so that it is not necessary to employ any zinc salts. As a matter of fact, we have unexpectedly found that if appreciable concentrations of ammonium sulphate be substituted in the first bath for sulphuric acid, then the use of metallic sulphates can be eliminated and the thread is suiliciently coagulated introduced into the coagulating bath.

From the above it can be seen that satisfactory spinning of viscous filaments is possible with the omission of sulphuric acid or with sulphuric acid in very low concentrations in order to mainto the spinning whereby it except in the negative capacity of the degree to which they inhibit the reaction rate of sulphuric acid. On the other hand, ammonium sulphate is capable of coagulating viscose without the aid of acid or other ingredients. (Other ammonium salts may possess the same properties.)

Theoretically, pure cellulose xanthate can be stretched to an almost unlimited extent, and as the regeneration proceeds, the ability to stretch is correspondingly decreased. Therefore, the use of ammonium sulphate as a coagulant, has certain advantages over sulphuric acid, because as pointed out above, sulphuric acid in any concentration will tend to regenerate cellulose xanthate. It is to be pointed out, however, that as regeneration proceeds, the thread becomes less plastic and therefore its ability to stretch decreases, but as the plasticity is lowered, the micelles in the filaments tend to be more effectively oriented by stretching. Therefore, in order to effect a maximum strength or tenacity without impairing any of the'other characteristics of the thread, a definite relation and adjustment between the rate and degree of regeneration and stretch must be set up.

Consistent with the above principle, the present process provides for optimum spinning conditions. Using ammonium sulphate permits unlimited control and adjustment between the rate of regeneration and stretching, because it not only coagulates viscose similar to sulphuric acid,

but retards regeneration similar to metallic salts and to that extent acts as a substitute for both. Now in order to set up the optimum spinning conditions, the freshly coagulated cellulose xanthate thread is stretched between several points during regeneration and while the thread is passed through one or more hot regenerating baths. more suitable than one regenerating :bath when used in conjunction with a primary bath that serves to coagulate and initiate the regeneration of the thread. It is generally conceded that at least one regenerating bath should be maintained at a high temperature because the temperature accelerates the rate of regeneration, and also effects some swelling of the thread can be more suitably stretched. In case one regenerating bath is used, its composition may be generally the same as that used in the normal two-bath system (sulphuric acid in the first bath), i. e., approximately 1% sulphuric acid plus salts brought over from the first bath. In the case of using several regenerating baths, the first regenerating bath may contain approximately 1% sulphuric acid and the succeeding baths contain increasing concentrations of sulphuric acid.

More particularly with respect to the first bath, ammonium sulphate is the fundamental ingredient. This salt is used to coagulate the viscose thread and may be used alone, provided it is present in suflicient quantities, for example, more than 20%. Continuous spinning is effected by adding only sufiicient sulphuric acid to neutralize the alkali being brought in with the viscose. However, in order to represent the best conditions for the purposes of the present invention, from 1 to 3% sulphuric acid should be used, in which case, salts such as sodium sulphate and magnesium sulphate may also be employed. In any event, the ammonium sulphate content should not be less than from 8% to 10%. For example, in a bath containing 10% ammonium sulphate and 2% sulphuric acid, at least 20% sodium sul- A number of regenerating baths may be phate or equivalent salts should be used. Recapitulating, ammonium sulphate coagulates, the sulphuric acid maintains acidity and assists in coagulation, and sodium sulphate retards the regenerative action of the acid. It is obvious that by varying the relative concentrations of these ingredients, a thread. of any desired degree of regeneration can be effected. The limits for practical use of these ingredients are:

Per cent Ammonium sulphate 8-30 Sodium sulphate 8-20 Sulphuric acid 0-10 Excellent baths are those in which the sum of the concentrations of the salts and acids is about 30%. In general, it is not possible to use 2% to.3% sulphuric acid without getting considerable regeneration, although it is possible if there is a very high total salt content. With most of the ammonium baths, a range of poor spinning occurs when from 3% to 6% sulphuric acid is employed. At concentrations higher than 6%, a well-regenerated thread is obtained which may be suitable for certain purposes, but in any case, the salt content must be preadjusted.

More particularly with respect to the second bath or succeeding baths, its or their purpose is to gradually regenerate or complete the conversion of the xanthate to pure cellulose while simultaneously stretching the thread. This is accomplished by sulphuric acid in-the presence of salts if necessary. The bath may contain from 1% to 10% sulphuric acid, and the salt contentwill depend upon the rate of regeneration required.

The salts may also control certain other characteristics of the finished thread such as strength, brittleness, and cross section of the individual filaments. Furthermore, the concentration of the second bath may be varied in accordance with the change in temperature. At higher temperatures, less acid is required. The bath should be above 60 C. and preferably, the bath is maintained in C. to C. in order to assist the stretching operation. As previously stated, a higher temperature effects a swelling of the thread which permits a greater degree of stretching.

In order to effect a proper stretching when utilizingour ammonium bath system, it is obvious that a number of different types of systems may be employed. For example, the thread may be stretched at proper points by means of driven godets rotating at different peripheral speeds or by means of stepped rollers, or by means of free- 1 7' rotatable rollers of different size. One system tating at a higher peripheral speed thanthe first mentioned godet. It is obvious that, the composition of the coagulating bath will determine the initial regeneraiton oi the thread, the

control of which is unlimited due to the use of ammonium sulphate. Between the godets a second stretch is imparted simultaneous with the passage of thread through the regenerating bath. The stretching of the thread takes place during the neighborhood of '75 the thread is stretched n wi 1 'Wansition period from the xanthate fonn to the regenerated form whereby a certain adjustment of stretch takes place and provides a thread of maximum strength and minimum elongation. All concentrations are calculated as parts by weight of the bath. I

EXAMPLE A viscose solution having a composition of 8% cellulose and 7% sodium hydroxide, was extruded through spinnerets to form a thread of 120- filaments and 275 denier. The thread was passed through a bath containing 14% ammonium sulphate, 20% sodium sulphate and 1.5% sulphuric acid. The bath was C. After passing the thread through the bath,

maintained at 45 1 it was preliminarily stretched and then passed Table Tenacity grams/100 denier E Percent of stretch Dry Wet Elonga- Elongation strength gation The present invention is not intended to cover 4 stretching and a correlation of the rate of re-. generation with stretching, so that a final thread is obtained having a dry tenacity substantially greater than 3 grams per denier and a dry elongation at the breaking point of less than It is, to. be. understood that viscose rayon is intended to cover staple fibers and also films and heavy denier yarns such as those used for reinforcing rubber-like articles, cords for fish lines,

sails, tents and the like, i

What is claimed is: 1

1. A process for the manufacture of viscose rayon having a dry tenacity greater than 3 grams/denier and an elongation at the breaking point of less than 10% which comprises spinning viscose filaments in a coagulating bath containing at least 10% ammonium sulphate, sulphuric acid in an amount less than 3% and suihcient metallic salts to retard the regenerative action of the sulphuric acid, and stretching the filaments during regeneration thereof in at least one hot bath containing only such sulphuric acid and salts as are carried over by the thread from the first bath, which bath is maintained at a temperature in a range of 75 C. to 80 C.

2. A process for the manufacture of viscose rayon having a dry tenacity greater than 3 grams/denier and an elongation at the breaking point of less than 10% which comprises spinning viscose filaments in an aqueous bath consisting exclusively of more than ammonium sulphate to effect coagulation without substantial regeneration of the filaments, and stretching the filaments during regeneration thereof in at least one bath containing from 1% to 10% sulphuric acid and metallic salts, which bath is maintained at a temperature above 60 C.

3. A process for the manufacture of viscose rayon having a dry tenacity greater than 3 ing point of less than 10% which comprises spinning viscose filaments in a bath containing at least 8% ammonium sulfate, 1% to 3% sulphuric acid, and suiiicient metallic sulphates to maintain a total bath concentration approximating to effect coagulation without substantial regeneration of the filaments, and stretching the filaments during regeneration thereof in at least one bath containing from 1% to 10% sulphuric acid and metallic salts, which bath is maintained at a' temperature above C.

4. A process for the manufacture of viscose rayon having a dry tenacity greater than 3 grams/denier and an elongation at the breaking point of less than 10% which comprises spinstretch thereto, passing the filaments to a second regenerating bath containing approximately 2% sulphuric acid and maintained at approximately 75 C. and simultaneously effecting a second high stretch during passage of the filaments through the said bath and finally collecting the filaments in package form.

5. A process for the manufacture of viscose rayon having a dry tenacity greater than 3 grams/denier and an elongation at the breaking point of less spinning viscose filaments in a bath containing approximately 1.4% ammonium sulfate,- 2g 0 sodium sulfate and 1.5% sulfuric acid, to effect coagulation without substantial regeneration of the filaments while imparting a preliminary stretch thereto, passing the filaments to a plurality of regenerating baths, the first of which stretching the thread in each bath to an extent consistent with the fected thereby until effected.

6. A process for the manufacture of viscose rayon having a dry tenacity greater than 3 gram/denier and an elongation at the breaking point of less than 10% which comprises spinning viscose filaments in a bath containing only suiiicient ammonium sulfate and sulfuric acid degree of regeneration efcomplete regeneration is to effect coagulation without substantial regeneration of the filaments, said ammonium sulfate content being not less than 8%, passing the filaments to a plurality of regenerating baths, the

first of which contains approximately 1% sulfuric acid and the succeeding baths contain increasing concentrations of by the thread is regenerated to successively greater degrees, and each bath to an extent consistent with the dethan 10% which comprises.

sulfuric acid wherestretching'the thread in gree of regeneration efiected thereby until complete regeneration is effected.

7. A process for the manufacture of viscose rayon having a dry tenacity greater than 3 gram/denier and an elongation at the breaking point of less than 10% which comprises spinning viscose filaments in a bath containing only sufiicient ammonium sulfate and sulfuric acid to effect coagulation without substantial regeneration of the filaments, said ammonium sulfate content being not less than 8%, passing the filaments to a plurality of regenerating baths, the first of which contains approximately 1% of sul- 'furic acid and the succeeding baths contain increasing concentrations of sulfuric acid and. therefore, greater regenerating power, and stretching the thread in each bath, the amount of stretch applied in each bath diminishing as the thread is regenerated, the said amount of stretch applied in each bath being consistent with the degree of regeneration effected in said bath, the regeneration proceeding substantially 10 to completion in the last bath.

GILBERT I. TH'URMOND. EDWARD BRENNER. 

